The present invention relates to a method of controlling the growth of weeds by the application of a mixture of a phenoxypicolinamide compound and a partner herbicide; and to the compositions containing them.
Phenoxypicolinamide herbicides are disclosed in the literature, for example in European applications EP-A-878,128, EP-A-447,004 and WO 94/07368. Several classes of phenoxypicolinamide compounds are known, which include for example those substituted at the 2- and 3-positions of the phenoxy group. These two such classes are distinguished by the fact that previously only the 2-substituted compounds have been mixed with partner herbicides. Previously, in general it has not been suggested to prepare mixtures with the 3-substituted compounds.
However, it has now been discovered that there are specific herbicides which can be mixed with 3-substituted phenoxypicolinamide compounds.
However certain individual weed species constitute a serious problem and are insufficiently controlled by phenoxypicolinamide compounds. As a result of research and experimentation it has been found that the use of phenoxypicolinamide compounds in combination with one or more of these herbicides extends the spectrum of herbicidal activity. Therefore the said combination represents an important technological advance. The term xe2x80x9ccombinationxe2x80x9d as used in this specification refers to the xe2x80x9ccombinationxe2x80x9d of clomazone and diflufenican.
Surprisingly, it has been found that the combined herbicidal activity of phenoxypicolinamide compounds with one or more of these herbicides, for the control of certain weed species is greater than expected, without an unacceptable increase in crop phytotoxicity, when applied pre-emergence of the weed species, i.e. the herbicidal activity of phenoxypicolinamide compounds with one or more of these herbicides showed an unexpected degree of synergism, as defined by Limpel, L. E., P. H. Schuldt and D. Lamont, 1962, 1. Proc. NEWCC 16, 48-53, using the formula:   E  =      X    +    Y    -                  X        ·        Y            100      
where E=the expected percent inhibition of growth by a mixture of two herbicides A and B at defined doses.
X=the percent inhibition of growth by herbicide A at a defined dose.
Y=the percent inhibition of growth by herbicide B at a defined dose.
When the observed percentage of inhibition by the mixture is greater than the expected value E using the formula above the combination is synergistic. The unexpected synergistic effect gives improved reliability in controlling serious competitive weeds of many crop species, leading to a considerable reduction in the amount of active ingredient required for weed control.
Accordingly the present invention provides a method for controlling the growth of weeds (i.e. undesired vegetation) at a locus which comprises applying to the locus a herbicidally effective amount of:
(a) a phenoxypicolinamide derivative of formula I; 
and (b) a partner herbicide selected from the group consisting of isoxazoles, diones, ureas and hydroxybenzonitrile (HBN) herbicides.
It will be understood that the herbicides used in the method of the invention may form agriculturally acceptable salts or metal complexes which may themselves be used in the method.
Advantageous possible partner herbicides for use in the present invention include;
isoxaflutole, which is 5-cyclopropyl-4-(2-methylsulphonyl-4-trifluoromethyl)-benzoylisoxazole,
ketospirodox, which is 2-(2,3-dihydro-5,8-dimethyl-1,1-dioxospiro[4H-1-benzothiin-4,2xe2x80x2-[1,3]dioxolan]-6-ylcarbonyl)cyclohexane-1,3-dione and potassium salt,
mesotrione, which is 2-(2xe2x80x2-nitro-4xe2x80x2-methylsulphonylbenzoyl)-1,3-cyclohexanedione,
sulcotrione, which is 2-(2xe2x80x2-chloro-4xe2x80x2-methylsulphonylbenzoyl)-cyclohexane-1,3-dione,
isoproturon, which is 3-(4-isopropylphenyl)-1,1-dimethylurea,
bromoxynil, which is 3,5-dibromo-4-hydroxybenzonitrile
and ioxynil, which is 4 hydroxy-3,5-di-iodobenzonitrile.
The preferred partner herbicides are chosen from isoxaflutole, isoproturon and bromoxynil.
The phenoxypicolinamide derivative of formula (I) and partner herbicides are normally used in the form of herbicidal compositions (i.e. in association with compatible diluents or carriers and/or surface-active agents suitable for use in herbicidal compositions), for example as hereinafter described.
The amounts of the phenoxypicolinamide derivative of formula (I) and partner herbicide applied vary with the nature of the weeds, the compositions used, the time of application, the climatic and edaphic conditions and (when used to control the growth of weeds in crop-growing areas) the nature of the crops. When applied to a crop-growing area, the rate of application should be sufficient to control the growth of weeds without causing substantial permanent damage to the crop. In general, taking these factors into account, application rates from 15 g to 1000 g/ha of the phenoxypicolinamide derivative of formula (I) and from 0.005 kg to 3 kg of partner herbicide per hectare give good results.
The phenoxypicolinamide derivative of formula (I) and a partner herbicide in combination may be used to control selectivity the growth of weeds, for example to control the growth of those species hereinafter mentioned, by pre- or post-emergence application in a directional or non-directional fashion, e.g. by directional or non-directional spraying, to a locus of weed infestation which is an area used, or to be used, for growing crops, for example cereals, e.g. barley, field and dwarf beans, carrots, cotton, flax, oats, lucerne, maize, oil seed rape, onions, peanuts, peas, rice, rye, soybeans, sunflower, wheat and permanent or sown grassland before or after sowing of the crop or before or after emergence of the crop. For the selective control of weeds at a locus of weed infestation which is an area used or to be used, for the growing of crops, e.g. the crops hereinbefore mentioned, application rates from 15 g to 500 g/ha of the phenoxypicolinamide derivative of formula (I) and from 250 g to 3000 g of urea herbicide; 5 g to 200 g isoxazole or dione herbicides; and from 50 g to 1000 g of HBN herbicide, per hectare are particularly suitable.
According to a feature of the present invention, there is provided a method for the control of the growth of weeds by pre- and/or post-emergence application which comprises the application of (a) a phenoxypicolinamide derivative of formula (I) and (b) a partner herbicide at application rates from 30 g to 200 g/ha of (a) and from 500 g to 2000 g/ha of urea herbicide, from 20 g to 100 g of isoxazole or dione herbicide; and from 20 0 g to 600 g (a.i.)/ha of the HBN herbicide, to control a very wide spectrum of annual broad-leafed weeds and grass weeds in cereal crops, e.g. barley, oats, rye and wheat without significant permanent damage to the crop. The combined use described above offers both foliar and residual activity and consequently can be employed over a long period of crop-development, i.e. from pre-weed pre-crop emergence to post-weed post-crop emergence. In the method according to this feature of the present invention, application of the herbicides to control weeds in autumn-sown cereals is preferred.
Weed species which are particularly well controlled include Setaria viridis, Echinochloa crus-galli, Galium aparine, Abutilon theophrasti, Amaranthus retroflexus and Ipomoea purpurea. 
The phenoxypicolinamide derivative of formula (1) and a partner herbicide in combination may also be used to control the growth of weeds, especially those indicated below, by pre- or post-emergence application in established orchards and other tree-growing areas, for example forests, woods and parks, and plantations e.g. oil palm, rubber and sugar cane plantations. For this purpose they may be applied in a directional or non-directional fashion (e.g. by directional or non-directional spraying) to the weeds or to the soil in which they are expected to appear, before or after planting of the trees or plantations at application rates from 30 g to 1000 g, preferably from 100 g to 300 g of phenoxypicolinamide derivative of formula (I) and from 250 g to 3000 g of the urea herbicide, preferably from 500 to 2000 g; from 25 g to 500 g of an isoxazole or dione herbicide, preferably from 50 to 300 g; and from 100 g to 2000 g, preferably from 200 g to 1000 g of an HBN herbicide per hectare.
The phenoxypicolinamide derivative of formula (I) and a partner herbicide in combination may also be used to control the growth of weeds, especially those indicated below, at loci which are not crop-growing areas but in which the control of weeds is nevertheless desirable. Example of such non-crop-growing areas include airfields, industrial sites, railways, roadside verges, the verges of rivers, irrigation and other waterways, scrublands and fallow or uncultivated land, in particular where it is desired to control the growth of weeds in order to reduce fire risks. When used for such purposes in which a total herbicidal effect is frequently desired, the active compounds are normally applied at dosage rates higher than those used in crop-growing areas as hereinbefore described.
The precise dosage will depend upon the nature of the vegetation treated and the effect sought. Pre- or post-emergence application, preferably pre-emergence application, in a directional or non-directional fashion (e.g. by directional or non-directional spraying) at application rates from 15 g to 1000 g of the phenoxypicolinamide compound of formula (I) and from 0.005 kg to 3 kg of the partner herbicide per hectare are particularly suitable for this purpose.
By the term xe2x80x9cpre-emergence applicationxe2x80x9d is meant application to the soil in which the weed seeds or seedlings are present before emergence of the weeds above the surface of the soil. By the term xe2x80x9cpost-emergence applicationxe2x80x9d is meant application to the aerial or exposed portions of the weeds which have emerged above the surface of the soil. By the term xe2x80x9cfoliar activityxe2x80x9d is meant herbicidal activity produced by application to the aerial or exposed portions of the weeds which have emerged above the surface of the soil. By the term xe2x80x9cresidual activityxe2x80x9d is meant herbicidal activity produced by application to the soil in which weed seeds or seedling are present before emergence of the weeds above the surface of the soil, whereby seedling present at the time of application or which germinate subsequent to application from seeds present in the soil, are controlled.
Weeds that may be controlled by the method include:
Alopecurus myosuroides, Anagallis arvensis, Anthemis arvensis, Anthemis cotula, Apera spica-venti, Aphanes arvensis, Arenaria serpyllifolia, Avena fatua, Bromus sterilis, Cerastium holosteoides, Chenopodium album, Chrysanthemum segetum, Descurainea sophia, Erysimum cheiranthoides, Galeopsis tetrahit, Galium aparine, Geranium dissectum, Geranium molle, Lamium amplexicaule, Lamium purpureum, Legousia hybrida, Lolium multiflorum, Lolium perenne, Matricaria inodora, Matricaria matricarioides, Montia Derfoliata, Myosotis arvensis, Papaver rhoeas, Phalaris minor, Phalaris paradoxa, Poa trivialis, Polygonum aviculare, Polygonum convolvulus, Silene vulgaris, Spergula arvensis, Stellaria media, Veronica hederifolia and Veronica Dersica. 
The pattern of persistence of the phenoxypicolinamide derivative of formula (I) and a partner herbicide allows the method of the present invention to be practised by the time-separated application of separate formulations.